Strip-edge-based displacement of intermediate rolls in six-high rolling stand

ABSTRACT

A method for the strip-edge-oriented shifting of the intermediate rolls ( 11, 11 ′) in a six-roll rolling mill comprising respectively a pair of workrolls ( 10, 10 ′), intermediate rolls ( 11, 11 ′) and backup rolls ( 12, 12 ′), whereby at least the intermediate rolls ( 11, 11 ′) and workrolls ( 10, 10 ′) have devices for axial shifting cooperating with them and each intermediate roll ( 11, 11 ′) has a barrel elongated by the amount of the CVC-shifting stroke and a one sided setback (x) in the region of the strip edge. The method is characterized in that the upper intermediate roll ( 11 ) is shifted in the direction of the drive side AS) and the lower intermediate roll ( 11 ′) is shifted in the direction of the service side (BS)—or conversely—relative to the neutral shift position (S zw =0 mm) symmetrically to the rolling mill center (y—y) be respectively the same amount in the direction of their (x—x).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/EP 01/07998 filed 11 Jul.2001 and based upon German National application 100 37 004.7 filed 29Jul. 2000 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a method of and an apparatus for thestrip-edge-oriented shifting of the intermediate rolls in a six-rollrolling mill, comprising respectively a pair of work rolls, a pair ofintermediate rolls and a pair of back-up rolls, whereby at least theintermediate and work rolls cooperate with devices for axially shiftingthem and each intermediate roll has a barrel elongated by the CVC(continuous variable crown) shifting stroke with a one-sided setback orground-back region in the region of the strip edge.

BACKGROUND OF THE INVENTION

The quality requirements of cold-rolled strip with respect to thicknesstolerances, the attainability of certain final thicknesses, stripprofiles or cross sections, strip planarities, etc. are continuouslyincreasing in the course of developments. As a consequence of suchdevelopments, the requirements for flexible rolling mill concepts andmodes of operation are likewise increasing and are required to beoptimally matched to an end product to be rolled.

For the classical rolling mill types referred to as quarto or four-highmills and six-high or sexto mills there are aside from basic conceptswith bending systems and fixed roll barrel shapes as roll gapinfluencing elements, two significant further rolling mill conceptswhich additionally affect the rolling gap by shifting of the workingrolls or intermediate rolls based upon different effective principles.These are:

CVC/CVC-plus Technology and

The technology of strip-edge-oriented shifting of rolls.

Up to now both of these technologies have required different rollingmill concepts because different roll geometries were required for them.

In the classic CVC or continuous variable crown technology, thebarrel-shaped lengths or contour lengths of the shiftable rolls wasalways longer than those of the fixed unshift-able rolls by the axialshifting stroke. The shiftable rolls thus need not have had their barrelterminating edge shifted beneath the stationary roll barrel. Thussurface damage or marking is avoided.

By contrast in the technology of strip-edge-oriented shifting, in theentire set of rolls, rolls with identical barrel or contour lengths areused. The shiftable rolls are thus shaped at the one side in the barreledge region with a corresponding geometry, especially they can beprovided with a taper. As a result, locally arising load peaks can bereduced.

The effective principle depends upon the strip-edge-orientedreadjustment of the barrel edge, either ahead of, or at, or even behindthe strip edge. Especially in the case of six-roll rolling mills, theshifting of the intermediate rolls beneath the backing roll gives riseto a targeted influence on the effectiveness of the positive work rollbending.

OBJECT OF THE INVENTION

The invention has as its object to utilize both technologies through aunitary mode of operation in a rolling mill conceptualization withgeometrically identical roll sets.

SUMMARY OF THE INVENTION

To achieve this object, a method for the strip-edge-oriented shifting ofthe intermediate roll in a six-roll rolling mill is provided inaccordance with the invention in which the upper intermediate roll isshifted in the direction of the drive side AS) and the lowerintermediate roll is shifted in the direction of the service side(BS)—or conversely—relative to the neutral shifting position (S_(zw)=0mm)), symmetrically with respect to the middle of the rolling mill byrespectively the same amounts in the direction of their axes.

By the use of intermediate rolls with filled setbacks or ground-backregions and strip-width dependent optimization of the axial shiftingpositions, the effectiveness of the positive work roll bending can beinfluenced in a targeted manner. Thus the roll gap can be optimally set.

In a refinement of the process, through the shifting of eachintermediate roll, the beginning of the recess is positioned externallyof, or at, or within the strip edge, i.e. within the strip width.

And finally, the method provides that the shifted positions in differentstrip width regions are given piecemeal (piece-by-piece) by linearexpressions or functions which relate different positions of thebeginning of the start to the strip edge.

An intermediate roll for strip-edge-oriented shifting with two-sidedelongated roll barrels or contours on the two sides, especially forcarrying out the method according to the invention is characterized inthat they each have elongated barrels extended by the CVC stroke whichare symmetrical with respect to the neutral shift position (S_(zw)=0 mm)at the rolling mill center.

As a basis for the rolling mill concept with intermediate rolls forstrip-edge-oriented shifting with two-sidedly elongated roll barrel, theroll configuration from CVC/CVC-plus-technology for a six-roll rollingmill is used.

As a refinement of the intermediate roll for strip-edge-orientedshifting with two sides elongated rolling contours provides that thebarrel at the service side (BS) is provided with the setback (x) orground back region, whose length (l) is subdivided into two adjoiningregions a and b as to which the following equations apply:

Region a: x = {square root over (R² − (R − d)²)} y(x) = R − {square rootover (R² − (1 − x)²)} Region b: x = 1 − a y(x) = d = const.R is the radius of curvature.

As a result locally arising load peaks are reduced, as is based upon theeffective principle of the strip-edge-oriented reshifting of the barreledge, either ahead of or to or to a location behind the strip edge.Especially in the case of six-roll rolling mills, the shifting of theintermediate rolls beneath the backing rolls gives rise to a targetedinfluence on the effectiveness of positive work roll bending.

An intermediate roll is further characterized in that the transitionbetween the recess (x) between the regions a or b, for example for agiven length a of 100 mm is effected with a sequential setback of themeasurement d in accordance with the following table:

Over a:

x 10 d/512 20 d/256 30 d/128 40 d/64 50 d/32 60 d/16 70 d/8 80 d/4 90d/2 100  d

And finally, a refinement of the rolling mill in accordance with theinvention provides that the one-sided setback (x) is provided on theupper intermediate roll, preferably at the service side (BS) and on thelower intermediate roll at the drive side (AS) or inversely.

BRIEF DESCRIPTION OF THE DRAWING

Details, features and advantages of the invention are given in thefollowing description of several embodiments schematically illustratedin the drawing.

In the drawing:

FIG. 1 is a diagrammatic elevation of one half of a six-high millshowing a geometry of the intermediate roll without the roll setback orground-away region,

FIG. 2 is an elevational view of part of an intermediate roll showing aone-sided setback or ground-away region in the region of the barrel edgeof the intermediate roll,

FIG. 3 is an elevational view of a six-high mill for strip-edge-orientedshifting with elongated intermediate roll barrels; and

FIG. 4 is an elevational view of a set of different positions of theintermediate roll setback.

SPECIFIC DESCRIPTION

The intermediate roll shown in FIG. 1 is derived from the rollconfiguration of the CVC/CVC-plus-technology for a six-high rollingmill. FIG. 1 shows a work roll 10, an intermediate roll 11 and a backuproll 12. The shiftable intermediate roll has a barrel extended in lengthrelative to the other rolls by the amount of the CVC shifting strokewhich has a neutral shifting position at the /center of the rolling milldefined by the plane y—y.

FIG. 2 shows a one-sided ground-away region or setback x in the regionof the barrel edge 13 of the intermediate roll 11. The setback x has thelength l and the barrel of the intermediate roll 11 extends from thebarrel edge 13 up to the barrel center with the length B. The length ofthe setback x is divided into two adjoining segments. In the firstsegment a, the setback conforms to the circle equation(1−x)² +y ² =R ²

If a predetermined minimal required diameter reduction 2 d, dependentupon the external boundary conditions, for example, rolling force andthe thereby resulting roll deformation, is reached, the setback x willrun linearly up to the barrel edge 13. The diameter reduction is thus soprovided that the work roll can bend freely by the amount of the setbackx of the intermediate roll without a contact therewith in region b. Thelength l of the setback is subdivided into the regions a and b which canbe calculated from the equations.

The transition between region a and region b can be made with or withouta continuous transition.

With another transition function for a predetermined length a of 100 mm,a special setback of the dimension d resulting from the ablation orgrinding away can be effected according to the following table:

Over a:

x 10 d/512 20 d/256 30 d/128 40 d/64 50 d/32 60 d/16 70 d/8 80 d/4 90d/2 100  d.The predetermined function here is flatter in the transition region thana radius and is very much steeper at the ends. Because of reasons ofgrinding technology, the transition toward the cylindrical part is madewith a correspondingly greater break in the transition between a and b(about 2×d).

As can be seen from FIG. 3, in the normal case, the one-sided setback isprovided on the upper intermediate roll 11 at the service side BS and onthe lower intermediate roll 11′ at the drive side AS, although it,however, does not change the effective principle when one applies thesetback x of the upper intermediate roll 11 at the drive side AS and onthe lower intermediate roll 11′ at the service side.

By the axial shifting of the intermediate rolls 11, 11′, the beginningof the setback x can be positioned outwardly to, at, or inwardly of thestrip edges 14, 14′ as FIG. 4 shows. This positioning is effected as afunction of the strip width and material characteristics can be targetedat effectively setting a positive work roll bending. Positive shiftingof the intermediate roll 11 signifies that the upper intermediate roll11 is shifted in the direction AS and the lower intermediate roll in thedirection BS as can be determined from FIG. 3.

FIG. 4 shows positioning of the intermediate roll setback with: Shiftingof the intermediate roll outside the strip edge (m=“+”)

Shifting of the intermediate roll onto the strip edge (m=0)

Shifting of the intermediate roll within the strip edge (m=“−”)

In different strip width regions, the shift positions is predeterminedby piecemeal linear step functions which define definite positions ofthe beginning of the setback x relative to the strip width.

The most important advantage of the described rolling mill concept, withonly one geometrically identical roll set both CVC/CVC-plus-technologyof strip-edge-oriented shifting can be obtained. It is no longernecessary to have different roll types. Differences can reside only inthe nature of the grinding of the rolls, however for a CVD plus- orsetback x in accordance with the above-defined parameters.

1. A rolling mill comprising: a rolling mill stand having a verticalmedian plane, a service side on one side of said stand and a drive sideon an opposite side of said stand; a pair of horizontal work rolls insaid stand for rolling a workpiece in the form of a metal strip; arespective intermediate roll bearing upon each of said work rolls; arespective backing roll bearing upon each of said intermediate rolls,each of said intermediate rolls having a bearing region extended axiallybeyond the respective work and bearing rolls by an amount equal to adisplacement stroke of said intermediate rolls; one of said intermediaterolls being provided at only one end with a setback region turned towardone of said sides and the other of said intermediate rolls beingprovided with only one setback region turned toward the other of saidsides, each of said setback regions being divided into two mutuallyadjoining inner and outer regions a and b, the inner region a beingcurved and forming a flush transition with the respective outer regionb, each inner region a having a contraction following the trigonometricequation (1−x²)+y²=R², each outer region b extending from the respectiveinner region a to the end of the respective bearing region, the innerand outer regions a and b conforming to the equations Region a: x ={square root over (R² − (R − d)²)} y(x) = R − {square root over (R² − (1− x)²)} Region b: x = 1 − a y(x) = d = const,

where x and y are coordinates of points on the surface of theintermediate roll, R is a radius of curvature of the inner region a, 1is a length of the setback region, and d is an amount of roll diameterreduction.
 2. The rolling mill defined in claim 1 wherein a transitionof the setback between regions a and b in the case of a predeterminedlength of 100 mm for a follows a sequential reduction of the dimension daccording to the table Over a: x 10 d/512 20 d/256 30 d/128 40 d/64 50d/32 60 d/16 70 d/8 80 d/4 90 d/2 100  d.